The most common and popular rinse-added fabric conditioner products are liquid products. Rinse-added liquid softeners are easy to handle, e.g., easy to dispense and to measure. The liquid form also minimizes the potential for concentrated deposition of the softener on an area of a fabric to cause visible staining. Some automatic clothes washers built with an automatic fabric softener dispenser require the fabric softener in liquid form for proper dispensing.
On the other hand, liquid fabric softener compositions contain a high level of water. The traditional liquid fabric softener products normally contain about 90% to about 95% of water. These products require a great amount of packaging material, the transport of large weight (making shipping expensive), and large shelf space in the retail stores. Recent trends to produce concentrated fabric softeners, with the intention of reducing waste, have improved the environmental impact and decreased the water content in the liquid compositions to about 72% to 80%, which is still a significant amount of water. Parallel with the effort to increase the level of fabric softener active in the liquid composition, another significant improvement in the fabric softener art is the development of rapidly biodegradable fabric softener actives to improve the environmental friendliness of fabric softener products. The new actives consist mainly of cationic quaternary ammonium compounds containing long chain alkyl groups, with at least one ester functional group inserted in some or all of the long chain alkyl groups. Such cationic quaternary ammonium compounds are disclosed, e.g., in E. P. Appln 409,502, Tandela et al., published Jan. 23, 1991; Jap. Pat. Appln 63-194,316, filed Nov. 21, 1988; Jap. Pat. Appln. 4-333,667, published Nov. 20, 1992; Jap. Laid Open Publication 1,249,129, filed Oct. 4, 1989; U.S. Pat. No. 4,767,547, issued Aug. 30, 1988; U.S. Pat. No. 4,808,321, issued Feb. 28, 1989; E. P. Appln 243,735, published Nov. 4, 1987; and U.S. Pat. No. 5,066,414, issued Nov. 19, 1991, all said patents and patent applications being incorporated herein by reference.
Solid rinse-added fabric softener compositions containing biodegradable fabric softener actives are disclosed in U.S. patent application Ser. Nos. 07/881,979, Baker et al., filed May 12, 1992, for Concentrated Fabric Softener Composition Containing Biodegradable Fabric Softener and 08/261,317, Hartman et al., filed Jun. 16, 1994, for Method of Using Solid Particulate Fabric Softener in Automatic Dosing Dispenser, and U.S. Pat. No. 5,185,088, Hartman et al., issued Feb. 9, 1993, said applications and said patent being incorporated herein by reference. In general, it is disclosed that the solid fabric softener can either be added directly into the rinse bath, or pre-diluted with water into a liquid composition prior to its addition into the rinse bath. As discussed before, the benefits of solid compositions include: the compactness of the compositions permit the transport of less weight, making shipping more economical; less packaging is required so that smaller and more readily disposable containers can be used; there is less chance for messy leakage; and less shelf space is required in the retail stores.
When the solid softener composition is added directly into the rinse bath of an automatic clothes washer, normally a top-loading clothes washer, with a short rinse cycle of about 2 to about 4 minutes and with normally cold rinse water, the solid softener composition tends not to be thoroughly dissolved and dispersed, which can lead to concentrated residues being deposited on some part of some fabrics to cause unacceptably visible stains. Furthermore, when the fabric softener can only be added via a dispenser, such as is the case with most front-loading clothes washers, the fabric softener composition is preferably, or necessarily, in the liquid form to minimize residue build-up in the dispenser. Therefore, it is preferred that at home, the consumers pre-dilute by adding both diluted water and the solid compositions into available permanent containers, to form and store liquid products, that are ready for subsequent laundry treatment.
When the liquid compositions are thus reconstituted from solid compositions containing biodegradable cationic ester (preferably diester) quaternary ammonium fabric softener actives having ester groups in the alkyl chains, the softener actives are somewhat labile to hydrolysis, and the softener actives are degraded rather rapidly upon storage. Therefore, it is the purpose of this invention to provide solid particulate, granular fabric softening compositions containing biodegradable cationic diester quaternary ammonium fabric softener actives to which water can be added to form dilute or concentrated liquid softener compositions which are chemically stable upon long-term storage.